This paper exploits a unique data set to explore the importance of key contractual characteristics on the duration of employment tenure. The paper recognises the insights of the human capital and job-matching approaches in informing discussion on employment tenure. Nevertheless, this paper argues that features of the contractual arrangements between employer and employee have been under-emphasised. The paper demonstrates that key features of contracts such as job security develop simultaneously with tenure. A clear lock-in effect is observed in the results.